There are many known data processing systems comprising a set of "memory cards", at least one "administration and processing station" or "unit" and at least one "communications network" for communicating at least one "memory card" with at least one station.
In this description, "memory card" will be used to designate all types of card, also known as chip card, smart card or IC-card, including an electronic circuit and/or a passive element for storing digital data and possibly further enabling logical operations to be performed. All these cards will henceforth be referred to as "memory card" or simply "card".
These known systems-include memory cards which are usually cards each having at least one integrated circuit (so-called IC memory cards) forming a microprocessor comprising ROM, RAM, EPROM and/or EEPROM type memories, access to these memories being controlled by a programme stored in the integrated circuit. These known systems also include at least one administration and processing unit or station, which is external to the memory cards, and which has the capability to write and/or read in at least one zone (hereinafter called the "private" zone, or "limited access" zone) of some or all of the memory cards.
Such a station will hereinafter be called a "central administration and processing station or unit" when it has the right to modify limited-access zones on the memory cards, and a "secondary station" when it is not authorized to modify limited-access zones.
Ever since memory cards were devised, a number of applications of this technology have appeared.
A first known generation of memory cards employed a central station able to write secret information into the card, and a number of secondary stations from which it was possible to consult non-critical data stored in the card, i.e. data which did not include the possibility of revealing or eliminating secret information.
A second known generation of memory cards used principally for pay-TV systems (CPTV cards) had, for each card, a variable number of secondary stations each able to freely and exclusively deal with its own limited-access zone of the card. In pay-TV systems, the secondary stations are for example television programme emitting stations. Each secondary station is generally constituted by a specific service vendor or by a television programme emitting station.
To make the system safe, this memory card structure prevents (or renders hermetic) any communication between the different limited-access zones of the different principal administration units. Hence, any given television programme broadcasting station in principle does not have a right to access any limited-access zone of a card which is reserved for another television programme broadcasting station. For each new service vendor or each new television programme broadcasting station, it is necessary to open a new limited-access zone on the card.
To illustrate this, consider the following voluntarily-simplified situation.
Supposing a pay-TV subscriber X wishes to subscribe to three television channels A, B and C, he has to contact each of the three channels who, via the transmitted video signal, will register orders to open respective limited-access zones in the subscriber's card. In subscriber X's card, 4 limited-access zones will be opened, namely an "emitter zone" and three limited-access zones for the three channels A, B and C respectively. The limited-access zones will be opened by the central administration station which is the only station with the right to open new limited-access zones, in other words it is the only station having the overall right to manage the card's entire contents. This principle is used at present in the Eurocrypt pay-TV norm.
These known second-generation cards have the following drawbacks.
Because of the setting up of several pay-TV systems and several data distribution systems, the following limitations occur:
A. The known systems are based on classic data-processing systems, namely segmenting of a part of the memory into several zones each reserved for a specific user, the central station (service vendor) conventionally having identical access to each of the cards, like in the case of a computer which is connected up by entering its password.
B. The processing/administration models used are based on the possibilities which were available before the electronic messenger service era. The model has not been revised to take into account new possibilities offered by the existence of a flux of data between a video signal emitting station and each memory card (CPTV-card) inserted in a pay-TV subscriber's decoder.
C. The data distribution structures have turned out to be much more complex than the originally-envisaged simple models, hence complicating administration while considerably limiting its flexibility.
D. The fact that for pay-TV there is principally a one-way flux between the operator and the memory card means that one can never be certain if the message has been well received, which creates difficult-to-simulate operating difficulties.
Such limitations set out above under headings A, B, C and D will be further explained in the subsequent description with reference to FIGS. 4 to 7.